Perplexing, but cf. Julius Pollux, Onomasticon 3.22.1, ὁ δὲ πατρὸς ἀδελφὸς θεῖος ἢ ἀδελφόθεος ἢ πατράδελφος ἢ πάτρως. So ἀδελφόθεος (which should literally mean "uncle on father's side") actually points to Jude's descent from (in pious early church opinion) Joseph's brother — Jude being the "other brother" of James, as in Matthew 13:55, or as here, the "brother of Joseph's brother's other son," or "step-brother through Joseph's previous marriage," depending on which dogmatic tradition you follow.
The whole title is quite ungrammatical, unless we have only part of it here. There's no "of" there — everything is nominative, except (possibly) ευσεβεεσσιους, which I'd really like to see in the manuscript. No way to make it εὐσεβέστατος, I don't suppose? For one thing, στ in ligature can very often look like σι. Any photos?